This invention relates generally to mapping or survey apparatus and methods, and more particularly concerns derivation of the azimuth output indications for such apparatus from the outputs or output indications of either an inertial angular rate vector sensor (or sensors) and an acceleration vector sensor (or sensors), or a magnetic field vector sensor (or sensors), and from the outputs of an acceleration vector sensor (or sensors).
U.S. Pat. No. 3,753,296 describes the use of a single inertial angular rate sensor, or "rate-of-turn-gyroscope", and a single acceleration sensor, both having their input axes of sensitivity nominally normal to the direction of travel in a borehole and parallel to each other for survey in a well or bore-hole. In this case, both sensors are rotated about an axis parallel to the borehole by either the carrying structure and container or by a rotatable frame internal to the survey tool. U.S. Pat. No. 4,199,869 describes the use of one or two dual axis inertial angular rate sensors in combination with a dual axis acceleration sensor for survey in a well or borehole. Again in this case, the sensors are rotated about an axis parallel to the borehole by either the carrying structure or by a rotatable frame internal to the survey tool. U.S. Pat. No. 4,244,116 describes the use of a one dual axis inertial angular rate sensor having its spin axis parallel to the borehole axis and one dual axis accelerometer for survey in a well of borehole. In this case no provision is made for rotation of the sensors about the borehole axis. U.S. patent application Ser. No. 338,261, filed Jan. 11, 1982 describes the use of one or more magnetic field vector sensors in combination with one or more acceleration sensors for survey with respect to the earth's magnetic field vector in a way related to the sensors of U.S. Pat. Nos. 3,753,296 and 4,199,869 which survey with respect to the earth's inertial angular rate vector.
The referenced patents and application describe the sensing equipments and show provisions to compute the output desired azimuth indication, but none of them show or teach the method and means described herein for obtaining the desired output, nor do they show the essential use of the output of the acceleration sensor (or sensors) to resolve the output (or outputs) of either the inertial angular rate sensor (or sensors) or the magnetic field sensor (or sensors) into a known coordinate system. For example, U.S. Pat. No. 4,244,116 shows a computation of: ##EQU1## where E=Vector of the earth rotation
.OMEGA..sub.z =Component of E along the borehole PA1 .OMEGA..sub.x, .OMEGA..sub.y =Gyro outputs normal to the borehole,
and states "the measurement .OMEGA..sub.x and .OMEGA..sub.y and the calculation of .OMEGA..sub.z give then the azimuth of the drilling line". This is in general not true since .OMEGA..sub.x and .OMEGA..sub.y are known only to be perpendicular to the drilling line, but are not known in a known earth fixed coordinate set.